Apparently I was so focussed on the phallic imagery in the book that I missed that Durmstrang is all boys and Beaux-Batons is all girls.
Not in the book, IIRC. Didn't a male student help the Beauxbatons teacher out of the carriage when they arrived? I guess it's just easier to put the two schools into matching uniforms (those BB grey outfits remind me a bit of Madeline, for some reason).